Chromosomal Alterations: Methods, Results and Importance in Human Health

525 Pages·2007·7.19 MB·English

by  Heidemarie Neitzel

Günter Obe ● Vijayalaxmi (Editors)
Chromosomal Alterations
Methods, Results and Importance in Human Health
Günter Obe
Vijayalaxmi (Editors)
Chromosomal Alterations
Methods, Results and Importance
in Human Health
With 99 Figures, 11 in Color, and 47 Tables
Professor Dr. Günter Obe Professor Dr. Vijayalaxmi
Gershwinstrasse 33 Department of Radiation Oncology
14513 Teltow The University of Texas
Germany Health Science Center
7703 Floyd Curl Drive
San Antonio, TX 78229
USA
Cover:
In Remembrance of Sarah
Chromosomal aberrations in a metaphase of cultured fibroblasts exposed to mitomycin C (50 ng/ml
for 24 hrs). Fibroblasts are from a girl with Fanconi anemia, complementation group FA-N, caused by
mutations in the PALB2 gene (Reid S et al., Nat Genet 39, 162-164, 2007). The checkpoint defect in
FA-N also leads to aneuploidy due to non-disjunction.
Sarah died from childhood cancer at the age of 12 months due to severe chromosome instability.
Library of Congress Control Number: 2007923871
ISBN: 978-3-540-71413-2 Springer-Verlag Berlin Heidelberg New York
eISBN: 978-3-540-71414-9 Springer-Verlag Berlin Heidelberg New York
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Preface
This book deals mainly with chromosomal alterations which represent
changes in the structure (chromosome mutations) or number (genome muta-
tions) of chromosomes and with sister chromatid exchanges (SCE).
Double-strand breaks (DSB) in DNA are the ultimate lesions for the for-
mation of chromosome mutation and SCE evaluated in the light microscope.
Typical chromosomal alterations are chromosomal aberrations (CA) and
micronuclei (MN). SCE result from repair of lesions during S phase (“true”
SCE), or from chromosome-type CA induced during G1 phase (“false” SCE).
Numerical alterations of chromosomes are discussed with respect to their
importance in clinical cytogenetics, to their ability to give rise to MN con-
taining whole chromosomes and to their origin during divisions of CA
containing cells.
Evaluation of chromosomal alterations, especially CA, MN and SCE, has long
been used in basic and applied research. Investigations into the mechanism(s)
of the origin of chromosomal alterations lead to insights into the structure and
function of chromosomes. Increased indices of chromosomal alterations in
cells, in vitro and in vivo, are used as indicators of exposure to biological,
chemical and physical genotoxins in our environment. Furthermore, elevated
genotoxicity has been correlated with increased carcinogenicity. This fits
with the observation of specific types of CA in cancer cells and with a positive
correlation between elevated frequencies of CA and cancer risk in human
populations.
DSB are induced directly by powerful DNA-damaging agents such as ioniz-
ing radiation and restriction endonucleases which lead to the formation of CA
in the same cell cycle stage in which the DSB are induced: in G0/G1 phase as
chromosome-type CA, in S phase as both chromosome-type and chromatid-
type CA (depending on whether DSB occur in unreplicated or in replicated
DNA, respectively) and in G2 phase as chromatid-type CA. Most genotoxic
agents induce DNA lesions other than DSB which during S phase lead to
chromatid-type CA and to “true” SCE.
CA, MN and SCE are analyzed in the light microscope after appropriate
staining (generally Giemsa stain). Special pretreatment of fixed metaphase
chromosomes on slides followed by staining with Giemsa stain leads to specific
banding patterns that allow in-depth analyses of specific types of CA such as
translocations and intra chromosomal and interchromosomal distributions
vi Preface
of CA. Application of fluorescence in situ hybridization (FISH) opened new
insights into unexpected complexities of CA. Following differential substitution
of chromosomal DNA with specific agents such as bromodeoxyuridine, SCE
can be made visible by staining with Giemsa stain. MN result from CA or
from whole chromosomes not distributed to the cell poles. Analyses of MN
are usually carried out in binucleate second-division cells after exposure to a
mutagen. FISH techniques are extremely useful to investigate mechanistic
aspects of the formation of MN.
The book starts with a chapter on structural and functional aspects of
human chromosomes. Chapters 2–8 describe DNA lesions leading to chro-
mosomal alterations (including gene mutations), and the ability of the cells
to repair such lesions. Chapters 9 and 10 explain how DNA damage can be
measured by means of γ-H2AX foci and by the comet assay. Chapters 11–14
explore mechanisms of the origin of CA (Chap. 11), the influence of nuclear
and chromatin structure on CA formation (Chaps. 12, 13) and CA and SCE in
telomeric regions (Chap. 14). Chapters 15–17 are devoted to MN and SCE.
FISH methods and their applications for the analysis of chromosomal alter-
ations are presented in Chaps. 18 and 19. In the following chapters topics
such as changing patterns of chromosomal alterations in ongoing cell cycles
(Chap. 20), human-population monitoring (Chap. 21), biological dosimetry
(Chaps. 22–24) and CA in peripheral lymphocytes of astronauts (Chap. 25)
are included. Chapters 26–29 are devoted to the question of possible carcino-
genic and chromosome-damaging effects of low- and high-frequency electro-
magnetic fields. The importance of chromosomal alterations in cancer cells
and as indicators of cancer risk in human populations is highlighted in
Chaps. 30 and 31.
We would like to thank our colleagues who generously and willingly con-
tributed to this book.
The editors hope that the book will serve as a textbook for graduate stu-
dents in biological sciences, residents in radiology and radiation oncology, as
well as researchers interested in occupational exposures, ionizing and non-
ionizing radiation, environmental mutagenesis and carcinogenesis.
January 2007
Günter Obe
Vijayalaxmi
Contents
1 Human Chromosomes: Structural and Functional Aspects . . . . . . . . . . . . . . . . . .1
HEIDEMARIENEITZELANDMARCTRIMBORN
1.1 History of Chromosome Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
1.2 Composition and Compartmentalization of Human
Chromosomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
1.3 The Human Karyotype and Clinical Cytogenetics . . . . . . . . . . . . . . . . . . . .5
1.4 Cell Cycle and Chromosome Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
1.5 Shaping the Metaphase Chromosome . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
1.6 Cohesion and Condensins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
1.7 DNA Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
1.8 Mendelian Disorders Affecting Chromosome Integrity . . . . . . . . . . . . . .14
1.8.1 Chromosome Instability Disorders . . . . . . . . . . . . . . . . . . . . . . . . .14
1.8.2 PCC Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
1.8.3 Further Syndromes Affecting Structural Maintenance
of the Chromosome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
2 DNA Lesions Induced by Ionizing Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
CLEMENSVONSONNTAG
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
2.2 Energy Deposition by Ionizing Radiation . . . . . . . . . . . . . . . . . . . . . . . . .23
2.3 Direct and Indirect Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
2.4 Cerenkov Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
2.5 Hole and Electron Transfer Through DNA . . . . . . . . . . . . . . . . . . . . . . . .25
2.6 Formation of Base Radicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
2.7 Base Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
2.8 Single-Strand Breaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
2.9 Double Lesions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
2.10 DNA–DNA Cross-Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
2.11 DNA–Protein Cross-Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
2.12 Clustered Lesions Beyond Double Lesions . . . . . . . . . . . . . . . . . . . . . . . . .34
2.13 Oxygen Effect and Chemical Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
2.14 DNA Damage by UV-C and Ionizing
Radiation – a Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
viii Contents
3 Effects of Ultraviolet Radiation on DNA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
JÜRGENKIEFER
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
3.2 Primary Photoproducts in DNA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
3.3 Action Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
3.4 Reversal and Repair of Primary Photoproducts . . . . . . . . . . . . . . . . . . . . .46
3.5 Cytological Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
3.5.1 Chromosomal Aberrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
3.5.2 Micronuclei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
3.5.3 Sister-Chromatid Exchanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
3.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
4 Double Strand Break Repair Mechanisms in Mammalian Cells . . . . . . . . . . . . .55
WOLFGANGGOEDECKE
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
4.2 NHEJ Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
4.2.1 NHEJ Mechanism and Junction Formation . . . . . . . . . . . . . . . . . . .56
4.2.2 Proteins Involved in NHEJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
4.3 DSB Repair by HRR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
4.3.1 HRR Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
4.3.2 Proteins Involved in HRR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
4.4 Impaired DSB Repair and Chromosomal Aberrations . . . . . . . . . . . . . . . .61
4.5 Fragile Sites Are Associated with DNA DSBs . . . . . . . . . . . . . . . . . . . . . . . .62
4.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
5 Backup Pathways of Nonhomologous End Joining May Have a
Dominant Role in the Formation of Chromosome Aberrations . . . . . . . . . . . . .67
GEORGEILIAKIS, WENQIWU, MINLIWANG, GEORGIAI. TERZOUDI,
ANDGABRIELE. PANTELIAS
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
5.2 Pathways of DSB Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
5.2.1 Homology-Dependent Pathways of DSB Repair . . . . . . . . . . . . . . .70
5.2.2 Homology-Independent Pathways of DSB Repair . . . . . . . . . . . . . .71
5.2.2.1 DNA-Dependent NHEJ . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
5.2.2.2 Backup NHEJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75
5.3 Homology-Independent End Joining and Chromosome
Aberration Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77
5.4 DSBs, NHEJ and Theories of Chromosome Aberration
Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
6 Targeted and Non-Targeted Induction of Chromosomal
Rearrangements After Exposure to Ionizing Radiation . . . . . . . . . . . . . . . . . . . .87
WILLIAMF. MORGANANDMARIANNEB. SOWA
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87
6.2 Radiation-Induced Chromosomal Instability . . . . . . . . . . . . . . . . . . . . . . .88
Contents ix
6.3 The Death-Inducing Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
6.4 Chromosomal Instability Induced by DIE Medium
from Unstable Clones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93
6.5 A Role for Non-Targeted Bystander Effects
in Radiation-Induced Chromosomal Instability . . . . . . . . . . . . . . . . . . . . .93
6.6 Implications of Non-Targeted Effects for
Cytogenetic Biodosimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94
6.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95
7 DNA Methylation Damage: Formation, Repair and Biological
Consequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
MARKUSCHRISTMANN, WYNANDP. ROOS, ANDBERNDKAINA
7.1 Methylating Agents as Environmental Carcinogens . . . . . . . . . . . . . . . . . .99
7.2 Anticancer Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
7.3 DNA Lesions, Sites of Attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
7.4 Repair of DNA Methylation Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104
7.4.1 Reversal Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104
7.4.1.1 Single-Step Repair by MGMT . . . . . . . . . . . . . . . . . . . . . .104
7.4.1.2 DNA Damage Reversal by AlkB Homologues . . . . . . . . .104
7.4.2 Mismatch Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
7.4.3 Base Excision Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
7.5 Mechanism of Mutagenicity and Carcinogenicity . . . . . . . . . . . . . . . . . . .108
7.6 Mechanism of Cytotoxicity of Methylating Agents by Apoptosis . . . . . .109
7.7 Mechanism of Formation of SCEs and Aberrations . . . . . . . . . . . . . . . . .111
7.7.1 Critical lesions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111
7.7.2 Involvement of MMR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112
7.7.3 Conversion Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113
7.7.4 Critical Role of Inhibition of Replication Fork Movement . . . . . .114
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115
8 Adducts, Sister-Chromatid Exchanges and Mutations Following
Benzo[a]pyrene Exposure: a Review of Quantitative Data Followed
by Some Considerations Regarding Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123
RINNEDEBONTANDNIKVANLAREBEKE
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123
8.2 Methodological Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .124
8.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125
8.3.1 Adducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125
8.3.1.1 BaP Exposure in Vitro: Dose–Effect Relationship
for Adduct Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . .125
8.3.1.2 Adducts in Vivo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127
8.3.1.3 BPDE Adducts Following BPDE Exposure . . . . . . . . . . .128
8.3.1.4 Human BaP Adducts in Vivo: Comparison
with Endogenous Adducts . . . . . . . . . . . . . . . . . . . . . . . .128
8.3.2 Sister-Chromatid Exchanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130
8.3.3 Mutations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131
x Contents
8.3.3.1 Mutations in Vivo in Animals Following
BaP Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131
8.3.3.2 Mutations in Vitro Following BaP Exposure . . . . . . .132
8.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132
8.4.1 Cancer Risk Associated with a Certain Level of BaP
Adducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .134
8.4.2 Supralinear Dose–Effect Relationship . . . . . . . . . . . . . . . . . . . .137
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
9 Analysis of DNA Double-Strand Breaks by Means of γ-H2AX Foci . . . . . . . .145
IRENASZUMIEL
9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145
9.2 Histone H2AX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .146
9.2.1 Histone H2AX Is Phosphorylated in Response
to Induction of DNA Double-Strand Breaks . . . . . . . . . . . . . .146
9.2.2 γ-H2AX Is Present in the Nuclear Foci . . . . . . . . . . . . . . . . . . .147
9.2.3 The Phosphatidylinositol 3-Kinase-Like
Protein Kinases Are the Main Enzymes that
Phosphorylate Histone H2AX . . . . . . . . . . . . . . . . . . . . . . . . . .147
9.2.4 Megabase Chromatin Domains Alter
Conformation After H2AX Phosphorylation . . . . . . . . . . . . . .149
9.3 Repair and Checkpoint Factors Are Recruited into γ-H2AX Foci . . . .149
9.4 Early DSB Rejoining Can Proceed Without Foci Formation . . . . . . . .150
9.5 Foci May Be Present Long After DSB Are Rejoined . . . . . . . . . . . . . . .150
9.6 Practical Aspects of γ-H2AX Estimation . . . . . . . . . . . . . . . . . . . . . . . . .151
9.6.1 Foci Size and Phosphorylation Heterogeneity . . . . . . . . . . . . .152
9.6.2 γ-H2AX Foci Frequency As a Measure of
Radiosensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154
9.6.3 γ-H2AX Foci Size and Frequency Depending
on Radiation Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
9.7 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158
10 Comet Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161
WOLFGANG-ULRICHMÜLLER
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161
10.2 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
10.2.1 Basic Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
10.2.2 Scoring of Comets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
10.2.3 Methods Aimed at the Detection of Specific Types
of DNA Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
10.2.4 Problem of Standardization of Methods . . . . . . . . . . . . . . . . . .165
10.2.5 Detection Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165
10.3 Factors That Might Affect the Outcome of Comet Analyses . . . . . . . . .166
10.3.1 Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166
10.3.2 Gender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166
Contents xi
10.3.3 Smoking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
10.3.4 Alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
10.3.5 Season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
10.3.6 Physical Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
10.3.7 Environmental Exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
10.4 Advantages/Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168
10.5 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169
10.5.1 Individual Radiosensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
10.5.2 Hypoxic Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
10.5.3 Genotoxicity of Chemicals and Identification
of Carcinogenic Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
10.5.4 Predictor of Cancer Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
10.5.5 Biomonitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171
10.5.6 Assessment of Exposure to Ionizing Radiation
in Vivo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171
10.5.7 UV Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172
10.6 Final Remark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172
11 Origin of Chromosome Aberrations: Mechanisms . . . . . . . . . . . . . . . . . . . . . .177
PETERE BRYANT
11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177
11.2 Primary DNA Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179
11.3 Models of Chromosome Aberration Formation . . . . . . . . . . . . . . . . . .181
11.3.1 The Breakage-First Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
11.3.2 The Molecular Misrecombination Model . . . . . . . . . . . . . . . . .185
11.3.3 The Transcription-Based Model . . . . . . . . . . . . . . . . . . . . . . . .186
11.4 Models of Chromatid Aberration Formation . . . . . . . . . . . . . . . . . . . . .187
11.4.1 Formation and Disappearance of Chromatid
Breaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187
11.4.2 Models of Chromatid Breakage . . . . . . . . . . . . . . . . . . . . . . . . .189
11.4.3 The Revell ‘Exchange’ Model . . . . . . . . . . . . . . . . . . . . . . . . . . .190
11.4.4 The Misrecombination Model . . . . . . . . . . . . . . . . . . . . . . . . . .192
11.4.5 The Signal Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193
11.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194
12 Chromatin Structure and the Formation of Chromosomal
Alterations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .201
GREGORKRETHANDCHRISTOPHCREMER
12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .201
12.2 Modelling of Virtual Radiation Events . . . . . . . . . . . . . . . . . . . . . . . . . .202
12.3 Modelling Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .203
12.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .208